1. Field of the Invention
The present invention relates to a magnetic recording device realizing multi-data recording.
2. Description of the Related Art
The development in high density recording and large capacity of a magnetic recording drive (Hard disk drive) influences the growth of a portable music media player and a video recorder in addition to a PC and a server. The degree of distribution of the magnetic recording device depends on the capacity of the magnetic recording device. The key point enhancing the capacity of the magnetic recording device almost depends on the enhancement of the recording density.
As an index relating to the recording density, a unit of bit number per square inch, that is, bit/inch2 (bpsi) is employed. As of now, the recording density is being enhanced by reducing the size per bit. With the bit size reduction, if the recording density reaches several Tbpsi, the line size per bit becomes 10 nm or less.
However, it is obvious the reduction in line size per bit by the conventional technique has its limitation as follows.
In order to read out small bits, the element size of a magnetic head to be employed is required to be downsized. Then, the element size of the magnetic head depends on the minimum line width limitation in photolithography technique. If the photolithography technique is developed so as to reduce the bit size, it becomes difficult the bit data stored in the corresponding bits formed in a magnetic recording medium are maintained originated from the heat fluctuation of the magnetic recording medium. Moreover, if a material with a higher magnetic anisotropy can be developed, bits formed at a magnetic recording medium made of the material can not be inverted by a magnetic head so that the intended magnetic recording can not be realized. In addition, if the bit size is set to 10 nm or less, the inherent magnetic feature of the material forming the magnetic recording medium can not be exhibited because the total number of atoms in the material contributing to the bit formation is decreased. In other words, if the material with the higher magnetic anisotropy is developed, the inherent magnetic feature of the material can be exhibited within a bit size range of 20 to 30 nm, but not within a bit size range of 10 nm or less.
According to the conventional technique of reducing the size per bit, the high density recording not only in the magnetic recording device but also in a storage device has its limitation in itself.
As described above, it is obvious the high density recording technique has its physical limitation by means of the reduction in bit size. In order to realize the high density recording not utilizing the reduction in bit size, multi-data recording and multi-layer recording can be exemplified as semiconductor memory technical field. In this case, since multiple data can be stored per area corresponding to 1 bit/1 pattern in the magnetic recording medium, the recording density can be enhanced.
It is difficult, however, to apply the multi-data recording technique and the multi-layer recording technique to the magnetic recording technical field, different from the semiconductor memory technical field.
With the multilayer recording technique, a semiconductor memory is configured such that a plurality semiconductor chips are stacked so as to be electrically connected with one another with electric wires. In this case, the multilayer recording can be realized by flowing a current selectively in one or more of the electric wires. In this case, it is required to form the multiple wires for realizing the electrical connection by means of minute processing technique. Since the minute processing technique is complicated, it is difficult to form the multiple wires, but the intended multi-layer recording can be realized in principle by the multiple wires.
In the magnetic recording device, however, no magnetic wire can be formed between the magnetic head and the magnetic recording medium. In this case, since it is required to dispose the magnetic head away from the magnetic recording medium, a minute space is formed between the magnetic head and the magnetic recording medium. In this point of view, the selective bit formation can not be realized using the magnetic wire so that some bits may be formed in the area of the magnetic recording medium in the vicinity of the magnetic head when intended bits are formed in the area away from the magnetic recording medium. Namely, suppose that the magnetic recording medium contains a plurality of recording layers, when the magnetic recording is carried out for the lower recording layer, the magnetic recording is also carried out for the upper recording layer so that some bits may be formed at the upper recording layer in addition to the lower recording layer. Therefore, the selective magnetic recording for the upper recording layer and the lower recording layer can not be realized. In the magnetic recording device, as a result, it is difficult to realize the multi-layer recording in principle.
With the multi-data recording technique, the bit information stored in the corresponding bit is recognized as a numeral “1” or “0” commensurate with the direction in magnetization of the bit. In order to realize the multi-data recording, in this point of view, it is required to set the direction in magnetization of the bit to zero degree meaning that the bit magnetization is oriented parallel to the surface of the magnetic recording medium, 45 degrees meaning that the bit magnetization is oriented in inclination from the direction perpendicular to the surface of the magnetic recording medium and the like. However, it is very difficult to realize the state where the bit magnetization is oriented parallel to the surface of the magnetic recording medium, the state where the bit magnetization is oriented in inclination from the direction perpendicular to the surface of the magnetic recording medium and the like. As of now, there is no technique to realize the above-described bit magnetization states. As a result, it is very difficult to realize the multi-data recording in the magnetic recording device.